The present invention relates to a direct-current motor of the electronic commutation type, for example, and comprising a permanent-magnetism element (such as a rotor, for example) which is provided opposite to an annular air-gap with at least two regions having opposite permanent magnetic polarities. This element is mounted for rotational motion relative to an electromagnetic element (such as a stator, for example) constituted on the one hand by at least one winding and on the other hand by at least one magnetic circuit which in turn comprises at least one yoke connected by means of arms surrounded in one case by the winding to at least two pole horns located opposite to the above-mentioned air-gap. The motor comprises in addition at least one auxiliary permanent magnet engaged within a spatial interval between two circumferential ends of the two pole horns, said ends being directed towards each other. The above-mentioned permanent magnet forms a longitudinal projection carried by a support housed within an inter-pole space provided between the yoke and the two adjacent horns.
By suitable current commutation within the winding, the pole horns interact magnetically with the permanent magnetic regions of the other element, thus giving rise to a torque which tends to produce rotation of one element with respect to the other. When the motor is at rest, the auxiliary magnet interacts with the permanent magnetic regions in order to return these latter to an angular position in which their magnetic axis is moved away from the axis of the pole horns. In fact, when the above-mentioned magnetic axes are in substantially coincident relation, excitation of the winding does not give rise to any significant torque and the auxiliary magnet thus constitutes a simple means for permitting startup of the motor simply by excitation of the winding without requiring any ancillary starting device.
German patent N.degree. DE-A-31 08 392 describes a practical application of this simple means. In this specification, a support is provided for each auxiliary magnet. At the time of assembly, each support provided with its auxiliary magnet is introduced individually in a longitudinal groove formed between the pole horns of the electromagnetic element. It is therefore necessary to place the auxiliary magnets within the electromagnetic element one by one. Furthermore, the electromagnetic element must have a special shape for the purpose of retaining the magnet supports. This not only entails the need for a special construction involving high capital cost but also reduces the useful surface area and consequently has the further effect of reducing the useful electromagnetic flux while at the same time disturbing the magnetic stator field.